Liquid meters are used for a variety of applications where it is desired to measure the flow rate or volume of a given fluid or gaseous material. Some are positive displace meters, meaning that a volume of liquid is displaced by the meter and thus the volume of the liquid passing through the meter is known. Other meters are inferential meters, meaning that the actual displacement of the liquid or gaseous material is not measured. An inferential meter uses some other characteristic other than actual displacement to measure flow rate or volume. Inferential meters sometimes have advantages over positive displacement meters, including smaller size. For either type of meter, it may be important to find methods of reducing the cost of the meter.
One example of a positive displacement meter is known as an axial meter, like that described in U.S. Pat. No. 5,447,062. The axial meter described in this patent measures the volume of a fluid or gaseous material by determining the number of rotations of the interlocked spindles inside the housing of the meter. The meter is comprised of a housing that defines a flow path. Interlocked spindles, which are rotating components. Inside the flow path rotate as liquid passes through the housing. Each rotation of a spindle displaces a known volume through the meter. A magnetic detector in the form of an exciter disk is used to detect the rotation of the spindles like that described in U.S. Pat. No. 6,250,151. Other types of detectors, such as a Hall-effect sensor, may also be countersunk into the housing of the meter to detect the rotation of the spindles as described in U.S. Pat. No. 6,397,686.
One example of an inferential meter is known as a turbine flow meter, like that described in U.S. Pat. No. 5,689,071. The turbine flow meter described in this patent measures the flow rate of a fluid or gaseous material by determining the number of rotations of a turbine rotor located inside the flow path of the meter. The turbine rotors are rotating components. The meter is comprised of a hollow housing that includes a turbine rotor on a shaft inside the flow path created by the housing. The housing is constructed out of a high permeable material, such as stainless steel.
In the example of the positive displacement and inferential meter above that includes sensors in the meter housing, as m enters the inlet port of the meter, the material passes through the rotating component causing the rotating component to rotate. The rotation of the rotating component is sensed by a sensor As the rotating component rotates, the sensor causes a a pulse stream to be generated in response. The pulses occur at a repetition rate (pulses per second) proportional to rotation of the spindles or turbine rotor and hence proportional to the measured volume and/or rate of material flow.
In some meters, the sensor is countersunk in a port that is drilled into the housing to be placed in close proximity to the rotating component for detection of rotation. However, the port that contains the sensor does not extend all the way through the housing to the inner portion so that the sensor is not exposed to the flow path. The sensor detects the rotation of the rotating components through the housing using an electrical or magnetic signal. Since the housing is constructed out of a high permeable material, the sensor must detect the rotation of the spindles or rotor vanes through the housing of the meter. One method to reduce the cost of the meter is to use a lower costhousing material since the housing material comprises a large majority of the material used in the meter. However, less costly materials, such as aluminum for example, have a low permeability thereby making it difficult or impossible for the sensor to detect the rotation of the rotating components through housing.
Therefore, it is desirable to find a technique to use a lower cost, lower permeable material for the housing of a meter without disturbing the performance of the sensor.